DC/DC converters comprising a so-called flying capacitor are known. In such DC/DC converters, such as are disclosed by US 2013/0119961 A1 for example, an actively drivable switching element, a capacitor and a further switching element are connected in series between two output terminal points forming an output for a DC output voltage. In this case, a half-bridge comprising an actively drivable half-bridge switching element and a further half-bridge switching element is connected in parallel with the capacitor. The center point of the half-bridge is connected to an input for a DC input voltage via an input inductor. The actively drivable switching element and the actively drivable bridge switching element are driven successively such that firstly the capacitor is charged to the DC input voltage via the input inductor and then the charged capacitor is connected in series with the input inductor. In this case, the electrical potential of the capacitor, i.e. of its electrodes, jumps, from which the designation as a flying capacitor originates. In the described known DC/DC converters comprising a flying capacitor, moreover, the input inductor may be used as a boost converter inductor for boosting the DC input voltage by virtue of the actively drivable switching element and the actively drivable bridge switching element being driven synchronously.
The jumping electrical potential of the capacitor results in limitations for the possible uses of a DC/DC converter comprising a flying capacitor.
DE 10 2011 085 559 A1 discloses a DC/DC converter comprising a parallel circuit formed by a capacitor with at least one chopper. Each chopper comprises a half-bridge comprising two actively drivable bridge switching elements, said half-bridge being connected in parallel with the capacitor. An input inductor is connected to the center point of the half-bridge. Furthermore, an additional half-bridge comprising two actively drivable bridge switching elements is connected in parallel with the capacitor, an output inductor being connected to the center point of said additional half-bridge. Moreover, the capacitor is connected in series with a stabilizing capacitor. A DC voltage source may be connected to each input inductor of the known DC/DC converter, wherein the DC input voltages present at different input inductors may differ from one another. A DC output voltage is output at the output inductor. In this case, the DC input voltages and the DC output voltage are present relative to a connecting line to which the stabilizing capacitor is connected. A further DC voltage source may be connected by supplementation of a further half-bridge with a further input inductor. As a result of the capacitor being connected in series with the further capacitor, it is necessary to convert in each case only the portions of the DC input voltages which are different, and the actively drivable bridge switching elements need only be designed for the portion of the DC input voltages which is converted. In order to keep the voltage at the stabilizing capacitor constant, however, the DC output voltage of the known DC/DC converter must always be a weighted average of the DC input voltages. In order to connect the known DC/DC converter to a link circuit having a relatively high link circuit voltage, it is therefore necessary to provide an additional boost converter, the components of which have to be designed for the full link circuit voltage and the entire power flowing via the DC/DC converter.
“Veerachary, M.: Two-Loop Controlled Buck-SEPIC Converter for Input Source Power Management. In: Industrial Electronics, IEEE Transactions on (Volume: 59, Issue: 11), 4 Nov. 2011, 4075-4087” discloses a converter topology which combines a buck converter for a voltage source having a relatively high voltage with a SEPIC converter for a voltage source having a relatively low voltage that is separated therefrom. The outputs of the buck converter and of the SEPIC converter are connected to one another, wherein the chopper inductor of the buck converter is connected to the input side of the output-side diode of the SEPIC converter.
“Gules, R. et al.: A modified SEPIC converter with high static gain for renewable applications. In: Power Electronics Conference (COBEP), 2011 Brazil, 11-15 Sep. 2011, 162-167” disclose a modified SEPIC converter comprising an additional diode and an additional capacitor in comparison with a traditional SEPIC converter. In this case, the capacitor is connected in series with the second inductor of the SEPIC converter, and the diode connects a node between the first inductor and the switch to a node between the second inductor and the additional capacitor of the SEPIC converter.
DE 10 2009 052 461 A1 discloses a buck converter for charging a divided DC voltage link from a photovoltaic generator. In this case, the buck converter comprises one buck converter switch, two buck converter diodes and two coupled buck converter inductors. One of the buck converter diodes and one of the buck converter inductors are respectively connected in parallel with one of two series-connected capacitors of the divided DC voltage link.